A clinical instrument is needed for accurate, repeatable measurements of corneal aberrations in patients with significant anterior segment abnormalities, such as cataracts, keratoconus, corneal scarring from previous corneal surgery, for example and specifically, scarring caused by sutures from previous penetrating keratoplasty (PKP) Retinal photography for this same population of the patient cannot be easily accomplished due to the scintillation and scatter caused by cataracts or corneal aberrations Our approach uses a state-of-the-art, patented technique in wavefront sensors and adaptive optics to address this problem in eye care. A technology based on diffraction-grating wavefront sensing (DG WFS) has been demonstrated by Kestrel Corporation in laboratory tests. This application proposes to apply the DG WFS technology to a portion of the patient population base from which it is difficult to obtain quality retinal images or for whom it is a significant challenge to make topographical measurements due to corneal aberrations The aim of the project is to compare wavefront measurements using standard wavefront technology based on Shack-Hartmann sensors with our diffraction grating-based sensor The ability of the DG WFS to make measurements where the Shack-Hartmann sensor breaks down will be demonstrated on human subjects with significant anterior segment aberrations (cornea and lens) or corneal scarring The commercial application is significant A fundus imager that will produce high quality, high resolution images of subjects with significant anterior segment abnormalities, such as cataracts, will have high demand in a market that relies heavily on imaging for diagnostic information Topographic measurements of this same patient population also represent a significant commercial application.